Port wine stain (PWS) is a congenital, progressive vascular malformation of human skin. The pulsed dye laser produces reasonably good clinical results in a limited population of patients due to its ability to destroy selectively PWS blood vessels. However, the degree of blanching achieved following laser therapy is variable and unpredictable, with the average treatment success rate below 10% if the ultimate standard required is complete blanching of the lesion. We hypothesize that this occurs primarily because the attending physician is unable to select optimal laser treatment parameters for a specific PWS lesion. Presently, all patients are treated using similar laser parameters, with selection based on clinical judgment of the physician, without taking into consideration individual variations in PWS geometry or optical properties of human skin. In particular, epidermal thickness and melanin absorption, as well as PWS blood vessel diameter and depth distribution vary on an individual patient basis and even between different areas on the same patient. A suitable imaging modality is needed to enable studies of relationships between individual PWS characteristics and response to therapy with varied treatment parameters. Our long-term goal is to develop a targeted approach to the clinical management of PWS patients receiving laser therapy on an individual patient basis. The clinical objective of PWS laser therapy is to maximize thermal damage to targeted blood vessels, while avoiding epidermal injury. Our central hypothesis in this research proposal is that infrared tomography (IRT) provides a practical methodology for PWS characterization prior to institution of laser therapy. In response to a sub-therapeutic diagnostic laser pulse, IRT provides a means to determine the initial space-dependent temperature increase in PWS skin which will enable the attending physician to apply optimal treatment parameters (light dosage, wavelength, pulse duration, and cryogen spurt duration) for each lesion, thereby avoiding epidermal damage while at the same time maximizing destruction of targeted blood vessels. In summary, the applicants believe that successful development and implementation of IRT should improve therapeutic outcome, reduce the number of treatment sessions, and improve the safety of PWS laser therapy.